Thermionic cathode



May M, 11950 D. c. PHIPPS THERMIONIC CATHODE Filed Aug. 12, 1946 l INVENTOR DARRELL C. DHIPPS ATTORNEY Patented May 16, 1950 UNITED STATES RATENT OFFICE THERMIONIC CATHODE British company Application August 12, 1946, Serial No. 689,881 In Great Britain August 17, 1945 Claims.

This invention relates to thermionic cathodes for electron discharge tubes, and more particularly but not exclusively to cathodes for cathode ray tubes.

In the manufacture of cathode ray tubes in which the cathode consists of a small cylinder closed at one end, where it carries the emissive coating, and open at the other end where it is supported in a structure of ceramic or like material, a heater coil being arranged inside the cylinder. Ceramic supports 1. e. made of molded and fired silicious material such as porcelain or steatite are preferred since such material may be molded and machined to a high degree of accuracy, whereby the mechanical placement of the electrode assembly of the cathode ray tube may be accurately predetermined. However, the disadvantage has presented itself that of two apparently identical structures the heating properties of the one differ from those of the other. In other words, when the steady state has been reached with a certain wattage of input current to the heater, the temperature of the emissive coating is diiierent in the one case from what it is in the other. It has been found that this variation between one specimen and another is due to variation in the quality of the mechanical junction between the open end of the cylinder and the support. Where there is a close fit between these two there occurs a greater leakage of heat away from the closed end so that in that case the final steady temperature is not so high as in the case where the fit is of a looser nature and the heat conductivity at the juncture is therefore smaller.

The object-of the present invention, therefore, is to provide means for ensuring greater uniformity in the steady temperature of thermionic cathode structures, said means rendering the quality of the join between the cathode and the supporting structure Of less importance as regards uniformity in heating properties. This object may be obtained in either or both of two ways.

One way consists of increasing the resistance to fiow of heat down the cylinder by forming the cylinder near this base with holes extending peripherally.

The other way consists in forming on the cylinder near the base a set of outwardly projecting fins which constitute a means by which heat can be radiated. These fins provide what may be described as a short-circuit on the juncture, that is to say, the radiation of heat from the fins is much greater than the leakage of heat by conduction to the ceramic. As this radiation is substantially constant as between one specimen and another,

the tubes are improved in the respect disclosed above. 7 The short-circuiting radiating means might take other forms: for example, it might consist of a downward extension of the cylinder below the ceramic support.

The invention will now be described with reference to the accompanying-drawing, which shows three embodiments of the invention by means of diametral sections. Each figure of the drawing shows a cathode structure I in the form of a cyl inder closed at one end, where it carries an emissive coating 2, and open at the other end, near to which it is attached to the ceramic support 5. A heater coil I is arranged inside the cathode structure I; the leads from the said heater coil 1 passing out through the open end of the said cathode structure. The join between the cath ode structure I and the ceramic support 5 is shown at 6. It is over the area of this join 6 that a variable rate of heat escape occurs, the rate of said heat escape depending on the quality of the said join 6.

In Figure l a radiating fin is shown attached, above the support 5, to the outside of the cathode structure I by the means of the weld 4. The purpose of this radiating fin 3 is to provide a heat radiating means short-circuiting the join 6. The area of this radiating fin 3 is large in comparison with the contact area of the cathode structure I and the ceramic support 5; hence the amount of heat radiated by the said fin 3 is likewise large in comparison to that passing by conduction from the cathode structure to the ceramic support and therefore the quality of the join 6 becomes of much less importance with the result that uniformity in the heating properties of cathode structures as from one tube to another is greatly increased.

In Figure 2 is illustrated another way in which this uniformity in heating properties can be obtained. A set of peripheral holes 8 is provided on the cathode structure I near the region of attachment to the ceramic support 5.

In Figure 3 is shown yet another embodiment of the invention in which the cathode structure I is carried below the ceramic support 5 to form extension 9 which constitutes a short-circuiting fin similar to the fin 3 in Figure 1.

I claim:

1. A thermionic cathode structure for an electron discharge tube comprising a metal cylinder closed at one end and open at the other, an emissive coating only on said closed end, an apertured ceramic disc support in which the open end of the said cylinder is received and clamped thereto,

a heating coil in the cylinder, and cooling means adjacent the support for controlling heat loss from the cylinder relatively to heat loss by conduction at the join to the ceramic disc support and so promotinguniformity in heating properties of such cathode structures.

2. A thermionic cathode structure for an electron discharge tube comprising a metal cylinder closed at one end and open at the other, an emissive coating only on said closed end, an apertured ceramic disc support in which the open end of the said cylinder is received and clamped thereto, a heating coil in the cylinder, and cooling means adjacent the support for controlling heat loss from the cylinder relatively to heat loss by conduction at the join to the ceramic disc support, said means comprising a heat-dissipating member projecting from said metal cylinder.

3. A thermionic cathode structure for an electron discharge tube comprising in combination a metal cylinder closed at one end and carrying an emissive coating only on said closed end, an apertured ceramic disc support in which the open end of the cylinder is received and clamped, a heat dissipating member extending outwardly from said cylinder, said heat dissipating member comprising a radiating fin providing heat loss large relatively to the heat loss by conduction through the join to the disc support.

4. A thermionic cathode structure for an electron discharge tube of the kind consisting of a cylinder closed at one end whereat an emissive coating is provided and open at the other end where it is joined to and supported in an apertured ceramic disc support by clamping to said support and containing a heater coil, and means on said cylinder adjacent said support [or promoting heat loss from the cylinder in an amount substantially greater than heat loss by conduction through the join, said means comprising a radiating fin formed on the cylinder where it constitutes a heat short circuit on the join to the supporting structure.

5. A thermionic cathode structure for an electron discharge tube comprising a metal cylinder closed at one end and open at the other, an emissive coating only on said closed end, an apertured ceramic disc support in which the open end of said cylinder is received and clamped thereto, a heating coil in said cylinder, and cooling means adjacent said support for controlling heat loss from the cylinder relative to heat loss by conduction at the junction of said cylinder to said ceramic disc support, said cooling means comprisin an extension of said metal cylinder beyond said support for dissipating heat by radiation.

DARRELL CECIL PHIPPS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,108,640 Bieling Feb. 15, 1938 2,372,037 Watrous Mar. 20, 1945 2,421,767 Varian June 10, 1947 

